Hydrogenation of a hydrocracked lubricating oil

ABSTRACT

The viscosity index of a hydrocracked lubricating oil stock boiling in the range of about 600*-1100* F. is increased by fractionating the stock into a light fraction boiling from 600* F. to about 750* F. and a bottoms fraction; mildly hydrogenating the light fraction and subsequently reblending the hydrogenated light fraction with the unhydrogenated fraction. Low boiling cracked hydrocarbons may be removed from the reblended lubricating oil to adjust the initial boiling point temperature to a desired value.

United States Patent Ashton et al.

Nelson, Nederland; Theodore C. Mead, Port Arthur, all of Tex.

Assignee: Texaco Inc., New York, NY.

Filed: June 25, 1973 Appl. No.: 373,332

Related US. Application Data Continuation-in-part of Ser. No. 129,231,Sept. 9, 1971, abandoned.

US. Cl 208/93, 208/18, 208/58 Int. Cl Cl0g 37/06 Field of Search 208/18,58, 93

References Cited UNITED STATES PATENTS 4/1957 Watkins et a1 208/58 [11]3,870,622 Mar. 11, 1975 3,642,610 2/1972 Divijak et a1. 208/58 3,666,6575/1972 Thompson et al 208/58 3,730,876 5/1973 Sequeira 208/18 [57ABSTRACT The viscosity index of a hydrocrac-ked lubricating oil stockboiling in the range of about 600-1100 F. is increased by fractionatingthe stock into a light fraction boiling from 600 F. to about 750 F. anda bottoms fraction; mildly hydrogenating the light fraction andsubsequently reblending the hydrogenated light fraction with theunhydrogenated fraction. Low boiling cracked hydrocarbons may be removedfrom the reblended lubricating oil to adjust the initial boiling pointtemperature to a desired value.

10 Claims, N0 Drawings HYDROGENATION OF A HYDROCRACKED LUBRICATING OILRELATED APPLICATIONS This application is a continuation-in-part ofcopending application Ser. No. 179,231, filed Sept. 9, 1971 nowabandoned.

BACKGROUND OF THE INVENTION The present invention relates to an improvedmethod for treating a hydrocracked lubricating oil stock to improve thetemperature-viscosity characteristics and oxidation stability thereof.More particularly, the present invention relates to a treating methodwherein a hydrocracked lubricating oil stock is fractionated into alight fraction with a maximum end point of 750 F. and a heavy fraction;the light fraction is subjected to a relatively mild hydrogenationtreatment; and the hydrogenated light fraction and heavy fraction arereblended to produce a lubricating oil stock with improvedtemperature-viscosity characteristics and improved oxidation stability.

It is known in the prior art to subject a lubricating oil stock to ahydrocracking reaction, and subsequently hydrogenate all or part of thehydrocracked oil to improve color and oxidation stability, reduceimpurities, neutralize the stock, and provide improvement in thelubricating oil stock temperature-viscosity characteristics. Thebenefits and advantages of such hydrocracking and hydrogenation oflubricating oil stocks are well known and understood by those familiarwith the prior art. For example, Watkins et. al. (US. Pat. No.2,787,582) discloses a process wherein a petroleum fraction (or crude)is fractionated into at least a 600950 F. virgin light lube stock and a950 F. residuum stock. The residuum stock is then hydrocracked.Hydrocracked effluent is subsequently fractionated into a light crackedhydrocarbon fraction, a 600-950 F. hydrocracked lube fraction and a 950F. hydrocracked fraction. The 950 F. hydrocracked fraction is recycledto extinction within the hydrocracking process, or alternatively may bedewaxed and deresined to yield a heavy lubricating oil stock. The600-950 F. hydrocracked fraction and the 600950 F. virgin fraction arecombined and treated in a very mild hydrogenation process, includingreaction temperatures of from about 100 F. to about 500 F. Thishydrogenated oil is then dewaxed and deresined to produce a lightlubricating oil product. As desired, light lubricating oil and heavylubricating oil may be combined to produce a desired lubricating oilproduct.

Other processes for treating a petroleum fraction to yield a lubricatingoil are show in Divijak et al. (US. Pat. No. 3,642,610) and Thompson etal. (U.S. Pat. No. 3,666,657). A full boiling range lubricating oilstock is hydrocracked at relatively severe conditions and thehydrocracked oil, in the lubricating oil range, is hydrogenated attemperatures in the range of about 550 F. to 800 F. Subsequently, thehydrogenated hydrocarbon effluent is dewaxed and deresined to yield afull boiling range lubricating oil product.

ln processes where a petroleum fraction is hydrocracked and subsequentlyhydrogenated to yield a lubricating oil stock, a substantial portionofthe oil in the lubricating oil range may be converted by crackingreactions, into undesirable lighter fractions. As petroleum oilssuitable for use in lubricating oils are in relatively short supply, itis desirable to minimize such losses. Also, hydrocracking andhydrogenating processes are expensive to construct and operate. Thus, itis desirable to have efficient operation of such pro cesses to obtainthe maximum benefit in improving lubricating oil quality.

The temperature-viscosity characteristic of importance in a lubricatingoil stock is the viscosity decrease with an increase in temperature.Such relationship between viscosity of the oil and its temperature maybe expressed in terms of a viscosity index number, wherein the viscosityindex number is determined by employing ASTM method 2270. Theviscosityindex number for lubricating oils expresses theviscosity-temperature relationship such that lubricating oils with lowerviscosity index numbers have relatively large changes in viscosity uponan incremental temperature change, and lubricating oils with higherviscosity index numbers have relatively smaller changes in viscosityupon an incremental change in temperature. Generally, lubricating oilswith higher viscosity index numbers are more desirable as such oils willmaintain their lubricating properties over a broader range oftemperatures. In hydrocracking and hydrotreating reactions, viscositydecrease is a roughjmeasure of the degree of cracking which a petroleumstock experiences. Excessive cracking results in a loss of lubricatingoil range hydrocarbons to lighter hydrocarbons. An increase in viscosityindex for a treated petroleum fraction improves the lubricatingproperties of the treated oil. Thus, processes for treating lubricatingoil stocks which produce a larger increase in viscosity index with aminimum decrease in viscosity of the treated oil are preferred.

Methods for increasing the viscosity index number for a lubricating oilstock are known, such as solvent extraction employing solvents such asfurfural, phenol, N-methylpyrrolidone and other solvents known to theart. Such solvent extraction methods improve the viscosity index numberof a lubricating oil stock by extracting therefrom components, such asaromatics, which have a relatively low viscosity index number. Byemploying such a solvent extraction process, a substantial portion ofthe lubricating oil stock may be removed and the yield of finishedlubricating oil is consequently decreased. Depending upon the nature ofthe lubricating oil stock subjected to a solvent extraction process, theyield of finished lubricating oil may be decreased by as much as 30% ormore.

SUMMARY OF THE INVENTION Now according to the method of the presentinvention, we have discovered an improved method for increasing theviscosity index number of a hydrocracked lubricating oil stock whichboils in the range of about 600 F. l,l0O F. without substantiallydecreasing the yield of finished lubricating oil. The method of thepresent invention comprises fractionating the hydrocracked lubricatingoil stock into a light fraction and a heavy fraction prior tohydrogenation. The light fraction boils in the range of about 600 F. toabout 750 F. Generally, such a light fraction of a lubricating oil stockcomprises from about 20% to about 30% by volume of the hydrocrackedlubricating oil stock. The light fraction only is subjected to a mildhydrogenation reaction at a temperature of from about 600 F. to about725 F., a pressure of from about 1,000 psig to about 20,000 psig withhydrogen in the presence of a hydrogenation catalyst. The hydrogenatedlight fraction is then reblended with the heavy fraction to produce alubricating oil of increased viscosity index number. If necessary, thereblended lubricating oil may be vacuumed stripped or otherwise treatedto adjust the initial boiling point. I

By following the method of the present invention, the viscosity indexnumber of a hydrocracked lubricating oil stock may be substantiallyincreased and the yield of hydrogenated lubricating oil stock will beabout 89 volume percent of the hydrocracked stock or higher.Additionally, by following the method of the present invention, theratio of viscosity index increase to viscosity decrease isgreater thansimilar process of the prior art where broad boiling range hydrocrackedlubricating oil stocks are hydrogenated. These and other advantages ofthe present invention will be more completely disclosed in the detaileddescription of the invention which follows.

DETAILED DESCRIPTION OF THE INVENTION Lubricating oil stock suitable fortreatment according to the method of the present invention compriseshydrocracked stocks boiling in the range of from about 600 F. to aboutl,lO F. and which have lubricating oil properties. For example,hydrocracked distillate fractions, hydrocracked deasphalted oils, andother oil stocks containing substantial concentrations of low molecularweight aromatic compounds boiling in the desired range may be employed.Such stocks generally contain substantial amounts of paraffinichydrocarbons of high molecular weight which adversely effect the pourpoint temperature of such stocks. To produce finished lubricating oils,such stocks are generally subjected to a dewaxing process, such assolvent dewaxing, propane dewaxing, or other known dewaxing processes toadjust the lubricating oil stock pour point temperature to the desiredvalue. Such dewaxing step may conveniently be performed prior to orsubsequent to treatment according to the method of the presentinvention. Preferably dewaxing, which is an expensive process, isperformed near the end of the process sequencerequired to produce afinished lubricating oil of desired properties. In this manner thedewaxing process may be performed on the minimum volume of oil, therebyreducing the cost of the process. The hydrocracked lubricating oilstocks contemplated for treatment according to the process of thepresent invention are those which contain substantial amounts ofrelatively low molecular weight aromatic hydrocarbons such as mono-,di-, and tri-nuclear aromatic compounds. The method of the presentinvention is particularly useful in treating a lubricating oil stockderived from a hydrocracked, deasphalted oil fraction boiling in therange of from about 600 F. to about l,l00 F. High molecular weightpolynuclear aromatic compounds generally present in heavier fractions ofpetroleum oils may be partially saturated in a hydrocracking reactionand then tend to crack before the last one or two rings are saturated.Therefore. low molecular weight aromatic compounds having a lowviscosity index number concentrate in the lighter fractions ofhydrocracked lubricating oil stocks.

It has been observed that when lubricating oil stocks are subjected to ahydrogenation reaction, the first ring of a particular poly-nucleararomatic will tend to saturate in preference to the aromatic rings ofcompounds of the same molecular weight range. containing fewer aromaticrings. For example, one ring of a tri-nuclear aromatic compound tends tobe saturated in a hydrogenation reaction before a ring of a di-nucleararomatic compound or a mono-nuclear aromatic compound of the samemolecular weight. Therefore, when a full boiling range lubricating oilstock comprising poly-nuclear aromatic compounds with a relatively largenumber of aromatic rings is treated in a hydrogenation reaction, therings of the highly aromatic poly-nuclear aromatic compounds tend topartially saturate and the aromatic rings of less aromatic compounds,particularly monoand di-nuclear compounds, tend to remain unsaturated.It has also been observed that such hydrogenation treatment of a highboiling range lubricating oil stock does not substantially improve theviscosity index number of such stocks. More severe hydrogenationtreatment of a full boiling range lubricating oil stock, in an effort tosaturate a significant number of the monoand di-nuclear aromaticcompounds, generally results in cracking a significant portion of thelubricating oil stock into compounds boiling below the lubricating oilrange. Thus, a severe hydrogenation treatment ofa hydrocrackedlubricating oil stock may result in a significant yield loss of finishedlubricating oil.

We have discovered that saturation of a significant portion of thearomatic rings of the lower molecular weight aromatic hydrocarbonscontained in a lubricating oil stock will substantially increase theviscosity index number of the resulting lubricating oil.

According to the method of the present invention, the lower molecularweight aromatic compounds of a hydrocracked lubricating oil stock arepreferentially saturated in a hydrogenation reaction and only a verysmall amount of the lubricating oil stock is cracked into hydrocarbonsboiling below the desired lubricating oil range. A hydrocrackedlubricating oil stock boiling in the desired lubricating oil boilingrange of from about 600 F. to about l,l00 F., is fractionally distilledinto a low boiling fraction and a high boiling fraction. The fractionaldistillation of the lubricating oil stock is controlled so that thearomatic compounds contained in the light fraction comprise essentiallymono-, di-, and tri-nuclear aromatic compounds. To obtain a lightfraction comprising mono-, di-, and tri-nuclear aromatic compounds, theend point of such light fraction is limited to about 750 F., andpreferably is limited to about 725 F. That is, the light fraction boilsin the range of about 600 F. 750 F. Any convenient fractionaldistillation means capable of providing the desired separation may beemployed.

The light fraction recovered from the fractional distillationstep istreated in a relatively mild hydrogenation reaction under conditionswhich favor saturation of aromatic compounds. Catalyst which may beemployed in the hydrogenation reaction comprise those catalyst which aresuitable for hydrogenating aromatic compounds and which do not have asubstantial cracking activity. Examples of such catalysts includechromium, tungsten, cobalt, molybdenum, nickel. their oxides andsulfides, and combinations thereof. Also, catalytically active noblemetals such as platinum, palladium, rhodium, irridium, ruthenium, andcombinations thereof may be employed. However, the noble metal catalyststend to be poisioned by compounds commonly present in lubricating oilstocks, particularly sulfur and nitrogen compounds. Hydrogenationcatalyst square meters per gram comprising about 5.9 weight percentnickel and about 18.3 weight percent tungsten supported upon an aluminumoxide base. A preferred catalyst which may be employed in thehydrogenation step of this invention is a pelletized catalyst having asurface area of about 287 square meters per gram comprising about 10.7weight percent molybdenum and about 2.8 weight percent cobalt supportedupon an alumina base. Preferably such catalysts are employed in theirsulfide form which may be obtained by methods well known in the art suchas treatment at elevated temperatures with hydrogen streams containinghydrogen sulfide or with oil streams containing small concentrations ofcarbon disulfide.

1n the hydrogenation step of our invention, the optimum reactiontemperature will vary somewhat depending on the catalyst employed. Thedesired reaction temperature is that at which a substantial portion ofthe aromatic components of the light fraction are saturated and at whichonly a very small portion of the light fraction is cracked intocomponents boiling lower than the desired lubricating oil boiling range.Hydrogenation temperatures of from about 600 F. to about 725 F. aresuitable and preferably temperatures are from about 650 F. to about 700F. Lower temperatures may be employed when noble metal hydrogenationcatalysts are employed. Other operating conditions in the hydrogenationstep include a pressure of between about 1,000 and about 10,000 psig,and preferably from about 1500 to about 3000 psig, a liquid hourly spacevelocity from about 0.1 to about 3.0 and preferably from about 0.5 toabout 1.5 volumes of hydrocarbon per volume of catalyst per hour, and ahydrogen feed rate from about 500 to about 30,000 standard cubic feetper barrel of lubricating oil stock or higher and preferably from about5,000 to about 20,000 standard cubic feet per barrel. It is notnecessary that the hydrogen employed in the hydrogenation step be 100%pure, and hydrogen rich streams of the type generally available inrefinery type operations, e.g., of about 70% or higher hydrogen content,are acceptable. The particular operating conditions to be employed inthe hydrogenation reaction in any specific operation will vary to acertain extent depending upon the properties of the light fraction beingtreated and upon the type of catalyst employed. The purpose of thehydrogenation step is to saturate a substantial portion of the lowermolecu lar weight, i.e., monoand di-nuclear aromatic, compounds presentin the light fraction. Operating conditions may be adjusted by oneskilled in the art to obtain the optimum saturation of such aromaticcompounds.

A mixture of hydrogenated light fraction and noncondensed gas isrecovered from the hydrogenation step. The noncondensed gas is separatedfrom the light fraction by any convenient vapor liquid separation meanssuch as for example a high pressure separator wherein the noncondensedgases are removed overhead and the hydrogenated light fraction liquid iswithdrawn as a liquid stream. A portion of the noncondensed gases fromthe vapor liquid separation means may be returned to the hydrogenationreaction as a hydrogen recycle stream. A portion of such noncondensedgas may also be vented to remove from the system any small amount of lowmolecular weight hydrocarbon gases formed in the hydrogenation step.Fresh hydrogen is conveniently added to the recycle hydrogen stream asmakeup for the hydrogen consumed in the hydrogenation step and for thatvented to remove light hydrocarbons.

From the vapor liquid separation means, the hydrogenated light fractionis combined with the heavy fraction of the lubricating oil stockrecovered from the fractionation step. The combined stock is thentreated to adjust the initial boiling point to the desired value byremoving any small amount of low boiling cracked products therefrom. Forexample, the combined stock may be heated to a temperature about 340 F.at a pressure of about 3 milimeters mercury absolute, where upon the lowboiling cracked hydrocarbons will be vaporized and the initial boilingpoint of the combined stock may be adjusted to a desired value of about600 F. Other means, such as fractional distillation, may also beemployed to adjust the initial boiling point of the combined stock tothe desired value.

Upon adjustment of the initial boiling point of the combined stock, afinished lubricating oil is produced having an increased viscosity indexnumber and improved oxidation stability over the lubricating oil stockemployed for treatment according to this invention.

In order to obtain the desired yield of finished lubricating oil ofabout 89 volume percent or more based upon the lubricating oil stock, ithas been found that the hydrogenated light fraction must be combinedwith the heavy fraction before the low boiling cracked hydrocarbon isremoved. Otherwise, if the hydrogenated light fraction is treated underconditions to vaporize the low boiling cracked hydrocarbon, asubstantial amount of hydrocarbon boiling within the desired lubricatingoil range will also be vaporized and thereby lost from the finishedlubricating oil product. The addition of the heavy fraction to thehydrogenated light fraction tends to maintain the desirable componentsof the light fraction in the liquid phase during the treatment to removeundesirable, low boiling cracked compounds therefrom.

EXAMPLE I A deasphalted vacuum residuum oil was hydrocracked underhydrocracking conditions of about 1800 psig pressure, a liquid hourlyspace velocity of 1.0 volumes ofoil per volume of catalyst per hour,7,200 standard cubic feet of hydrogen per barrel of oil, at atemperature of about 825 F. in the presence of a catalyst comprisingabout 3% cobalt and about 11% molybdenum on an alumina-silica basehaving a surface area of about 287 square meters per gram, such catalystbeing sold by American Cyanamid Company under the designation of Aerol-lDS 1441. From the hydrocracking reaction, a hydrocarbon product wasrecovered and fractionated to obtain a fraction boiling in the range ofabout 600 F. to about l,l00 F. This fraction was subjected to a solventdewaxing step wherein the pour point was reduced to about 10 F. From thesolvent dewaxing step, a lubricating oil stock having a pour point of 10F., a kinematic viscosity at 100 F. of 18.81 centistokes and a viscosityindex of 90 was obtained.

The dewaxed, hydrocracked oil was subjected to fractional distillationin a laboratory vacuum distillation column to yield a light fractioncomprising 23.8 volume percent of the lubricating oil stock and havingan end point of about 710 F. as an overhead product and a heavy fractioncomprising 76.2 volume percent of the lubricating oil stock as a bottomsproduct. The light fraction was subjected to a hydrogenation reaction ata temperature of 700 F., a pressure of 1800 psig, a liquid hourly spacevelocity of 0.5 volumes of oil per volume of catalyst per hour, ahydrogen rate of 15,000 standard cubic feet of hydrogen per barrel oflight fraction, in the presence of a catalyst comprising 3.5 weightpercent nickel, 18.5 weight percent molybdenum supported upon an aluminabase with a surface area of about 150 square meters per gram, suchcatalyst being sold by American Cyanamid Company under the tradenameAero HDS-9A. From the hydrogenation reaction, a hydrogenated lightfraction was recovered free of non-condensed gases in a yield of about105 weight percent based upon the light fraction charge. Thehydrogenated light fraction was then combined with the heavy fractionrecovered from the fractional distillation step. The combined fractionswere then heated in a vessel equipped with a water cooled refluxcondenser at a pressure of about 3 millimeters mercury absolute to aliquid temperature in the vessel of 320 F. to remove low boiling crackedhydrocarbons formed in the hydrogenation reaction. The finishedlubricating oil recovered as a liquid from the vessel comprised a 98weight percent yield based upon the dewaxed lubricating oil stockcharged to the fractional distillation step. The finished lubricatingoil has a distillation range of about 600 F. to about 1,100 E, a pourpoint of about 10 F., a kinematic viscosity of about 19.53 centistokesat 100 F., and a viscosity index of 97. Thus, it can be seen that byfollowing the method of the present invention a substantial improvementin the viscosity index, from 90 to 97, of the lubricating oil stock wasobtained with only a minor loss in yield of finished lubricating oil.Also, the viscosity index increase was achieved without a concomitantdecrease in oil viscosity.

EXAMPLE 11 The dewaxed. hydrocracked oil of Example 1, having a pourpoint of 10 F., kinematic viscosity of 18.81 centistokes at 100 F., andviscosity index of 90 was vacuum distilled toyield a light fractionoverhead comprising 25 weight percent of the oil and a heavy fractionbottoms comprising 75 weight percent of the oil. The light fractionhaving an end point of about 725 F. was hydrogenated at a temperature of700 F., a pressure of 1800 psig, a liquid hourly space velocity of 1.0volume of oil per volume of catalyst per hour, at a hydrogen rate of7,100 standard cubic feet per barrel of light fraction, in the presenceof a catalyst comprising 5.9 weight percent nickel and about 18.3 weightpercent tungsten upon an alumina support having a surface area of about171 square meters per gram, such catalysts being sold by HarshawChemical Company under the designation Ni-4403E. From the hydrogenationreaction, a hydrogenated light fraction free of noncondensed gas wasrecovered in a yield of about 91 weight percent based upon lightfraction charged. The hydrogenated light fraction was then combined withthe heavy fraction recovered from the fractional distillation step andthe mixture was charged to a vessel equipped with a water cooled refluxcondenser. 1n the 'vessel the mixture was heated at a pressure of 3millimeters mercury absolute to a liquid temperature in the vessel of320 F. to remove low boiling cracked hydrocarbons.

A finished lubricating oil in a yield of 89.5 weight percent based uponthe lubricating oil stock charged to the fractional distillation system,was recovered from the vessel. The finished lubricating oil had aboiling range of from about 600 F. to about 1,100 E. a kinematicviscosity of about 18.6 centistokes at 100 F., a pour point of 10 F. anda viscosity index of 100.

From Example 2, it is seen that, by following the fractionation andhydrogenation methods ofthe present invention, a substantial improvementin the viscosity index, from to 100, was obtained for the hydrocrackedoil with only minor decrease in viscosity. Also, the yield oflubrication oil, based upon hydrocracked oil is high (89.5%).

The finished lubricating oils of Examples 1 and 2 had good oxidationstability, and upon standing showed no tendency to form solidprecipitates which commonly occur in unstablized hydrocracked oils inthe lubricating oil range.

EXAMPLE "I This comparative example is to show the advantages of theprocess of the present invention over methods of the prior art, such asshown in Watkins et. al. (US. Pat. No. 2,787,582).

A wax distillate petroleum fraction is obtained by fractionation ofcrude petroleum. The wax distillate" has a viscosity of 96.1 centistokesat F., viscoity index of 69'and pour point temperature of 100 F. The waxdistillate" is hydrocracked and the hydrocracked oil is thenhydrogenated to yield lubricating oil stock of improved viscosity.

In the runs of this example, the wax distillate" is hydrocracked and thehydrocracked oil is fractionated into a 600 F. 950 F. boiling range oilstock. The oil stock is then separated into two portions for comparativehydrogenation runs to demonstrate the advantages of the presentinvention. A first portion of the 600 F. 950 F. oil stock ishydrogenated at particular hydrogenation conditions and the hydrogenatedoil is vacuum distilled to yield a first 600 F. 950 F. lubricating oilstock.

Following the method of the present invention, the second portion of the600 F. 950 F. oil stock is fractionated into a 600 F. 725 F. fractionand a 725 F. 950 F. bottoms fraction. The 600F. 725 F. fraction ishydrogenated at the same conditions as the hydrocracked first portiondescribed above. Effluent from this hydrogenation is combined with the725 F. 950 F. bottoms fraction and this mixture is vacuum distilled toyield a second 600 F. 950 F. lubricating oil stock.

Tests are performed on the first and second lubricating oil stock todetermine physical properties which relate to quality of lubricatingoils. Comparisons are drawn between properties of the lubricating oilstocks to demonstrate the advantages of the method of the presentinvention over the prior art.

Table 1 shows results from high temperature, low space velocityhydrocracking and low temperature, low space velocity hydrogenationoperations.

9 10 TABLE I Hydrocracking Hydrogenation 600-950F 600725F 600950FFraction Fraction Fraction Temperature (F) 775 700 775 Pressure (psig)1500 1500 1500 LHSV 0.25 0.25 0.25 (vol oil/hr/ vol catalyst) Hydrogento oil 5000 5000 5000 SCF/B Catalyst Harshaw Ni-4403E Product PropertiesFor 600-950 F. Range Oils Kinematic Viscosity 28.55 2900* 27.75(centistokes at 100F) Viscosity Index 1 I8 125* 12] Yield wt% 68 67*55.9 (basis wax distillate) Pour point temp. (F) 100 100* 100hydrogenation effluent recombined with 7Z5-J50F. fraction and mixturevacuum stripped to yield bll(l-950F. range oil.

From Table l, the advantages of employing the method of the presentinvention over the prior art method is clearly seen. The viscosity indexof the hydrocracked oil is substantially increased by hydrogenating the600-725 F. fraction, without a concomitant decrease in viscosity. Also,the yield of 600-950 F. lubricating oil stock is substantially increasedover the yield obtained by hydrogenating the 600950 F. rangehydrocracked stock.

Table 11 shows results from high temperature, low space velocityhydrocracking and hydrogenation operations.

stantially improved without the concomitant loss in yield of finishedlubricating oil which is generally experienced when methods of the priorart are employed.

To one skilled in the art it will be evident that many variations andmodifications of this invention can be practiced in view of theforegoing disclosure that will come within the spirit and scope of theinvention.

We claim:

1. A method of treating a hydrocracked lubricating oil stock having aninitial boiling point of about 600F, and having an end point in therange of from about hydrogenation effluent recombined with 725950F.fraction and mixture vacuum stripped to yield 600-95UF. range oil.

Table I] demonstrates the advantages of employing 950F to about L andContaining a antial the method of the present invention over the priorart method. The viscosity index of the hydrocracked oil is substantiallyincreased by hydrogenating the 600-725 F. fraction without a concomitantlarge decrease in viscosity. The hydrogenated 600950 F. fraction shows asubstantial viscosity decrease for a similar viscosity index increase.Yield of lubricating oil stock from the process of the present inventionis substantially higher of wax distillate) over yield (42% of waxdistillate) obtained by the prior art method.

By following the method of the present invention the viscosity index ofa lubricating oil stock may be subportion of mononuclear and di-nucleararomatic compounds, for increasing, the viscosity index thereof, whichmethod comprises:

a. fractionating the hydrocracked lubricating oil stock into a lightfraction boiling in the range of about 600F to about 750F, and a heavyfraction having an initial boiling point of about 750F;

b. hydrogenating the light fraction at a temperature of from about 600Fto about 725F, a pressure of from about 1,000 to about 10,000 psig, aliquid hourly space velocity of from about 0.1 to about 3.0 volumeslight fraction per hour per volume of catalyst with from about 500 toabout 30,000 standard cubic feet of hydrogen per barrel of lightfraction in the presence of a hydrogenation catalyst for saturation ofmono-nuclear and di-nuclear aromatics hydrocarbons; c. reblending thehydrogenated light fraction and the heavy fraction; and d. separatinglow boiling cracked hydrocarbon from the reblended lubricating oil ofstep (c) for adjustment of the initial boiling point to about 600F. 2.The method of claim 1 wherein the catalyst is selected from the groupconsisting of chromium, tungsten, cobalt, molybdenum, nickel, theiroxides, their sulfides, platinum, palladium, rhodium, irridium,ruthenium and combinations thereof.

3. The method of claim 2 wherein the hydrogenation upon alumina.

7. The method of claim 2 wherein the light fraction is hydrogenated at atemperature of from about 650F to about 700F, a pressure of from about1,500 psig to about 3,000 psig, a liquid hourly space velocity of fromabout 0.25 to about 1.5 volumes of oil per volume of catalyst per hour,and a hydrogen rate of from about 5,000 to about 20,000 standard cubicfeet of hydrogen perbarrel of light fraction.

8. The method of claim 7 wherein the hydrocracked lubricating oil stockis separated into a light fraction having an initial boiling point ofabout 600F and an end point of about 725F and a heavy fraction having aninitial boiling point of about 725F by fractional distillation.

9. The method of claim 8 wherein the initial boiling point temperatureof the reblended oil is adjusted to about 600F by vaporizing low boilingcracked hydrocarbons from the liquid reblended oil at an elevatedtemperature of about 340F and a subatmospheric pressure of about 3millimeters mercury, absolute.

l0. The'method of claim 9 including a dewaxing step to reduce the pourpoint temperature of the reblended oil to about 10 F. or less.

1. A METHOD OF TREATING A HYDROCRACKED LUBRICATING OIL STOCK HAVING ANINITIAL BOILING POINT OF ABOUT 600*F, AND HAVING AN END POINT IN THERANGE OF FROM ABOUT 950*F TO ABOUT 1,100*F, AND CONTAINING A SUBSTANTIALPORTION OF MONONUCLEAR AND DINUCLEAR AROMATIC COMPOUNDS, FOR INCREASING,THE VISOCOSITY INDEX THEREOF, WHICH METHOD COMPRISES: A. FRACTIONATINGTHE HYDROCRACKED LUBRICATING OIL STOCKING INTO A LIGHT FRACTION BOILINGIN THE RANGE OF ABOUT 600*F TO ABOUT 750*F, AND A HEAVY FRACTION HAVINGAN INTIAL BOILING POINT OF ABOUT 750*F; B. HYDROGENATING THE LIGHTFRACTION AT A TEMPERATURE OF FROM ABOUT 600*F TO ABOUT 725*F, A PRESSUREOF FROM ABOUT 1,000 TO ABOUT 10,000 PSIG, A LIQUID HOURLY SPACE VELOCITYOF FROM ABOUT 0.1 TO ABOUT 3.0 VOLUMES LIGHT FRACTION PER HOUR PERVOLUME OF CATALYST WITH FROM ABOUT 500 TO ABOUT 30,000 STANDARD CUBICFEET OF HYDROGEN PER BARREL OF LIGHT FRACTION IN THE PRESENCE OF AHYDROGENATION CATALYST FOR SATURATION OF MONO-NUCLEAR AND DI-NUCLEARAROMATICS HYDROCARBONS; C. REBLENDING THE HYDROGENATED LIGHT FRACTIONAND THE HEAVY FRACTION; AND D. SEPARATING LOW BOILING CRACKEDHYDROCARBON FROM THE REBLENDED LUBRICATING OIL OF STEP (C) FORADJUSTMENT OF THE INITIAL BOILING POINT TO ABOUT 600*F.
 1. A method oftreating a hydrocracked lubricating oil stock having an initial boilingpoint of about 600*F, and having an end point in the range of from about950*F to about 1,100*F, and containing a substantial portion ofmononuclear and di-nuclear aromatic compounds, for increasing, theviscosity index thereof, which method comprises: a. fractionating thehydrocracked lubricating oil stock into a light fraction boiling in therange of about 600*F to about 750*F, and a heavy fraction having aninitial boiling point of about 750*F; b. hydrogenating the lightfraction at a temperature of from about 600*F to about 725*F, a pressureof from about 1,000 to about 10,000 psig, a liquid hourly space velocityof from about 0.1 to about 3.0 volumes light fraction per hour pervolume of catalyst with from about 500 to about 30,000 standard cubicfeet of hydrogen per barrel of light fraction in the presence of ahydrogenation catalyst for saturation of mono-nuclear and di-nucleararomatics hydrocarbons; c. reblending the hydrogenated light fractionand the heavy fraction; and d. separating low boiling crackedhydrocarbon from the reblended lubricating oil of step (c) foradjustment of the initial boiling point to about 600*F.
 2. The method ofclaim 1 wherein the catalyst is selected from the group consisting ofchromium, tungsten, cobalt, molybdenum, nickel, their oxides, theirsulfides, platinum, palladium, rhodium, irridium, ruthenium andcombinations thereof.
 3. The method of claim 2 wherein the hydrogenationcatalyst is supported upon a porous, noncracking inorganic oxide base.4. The method of claim 3 wherein the base is selected from the groupconsisting of silica-alumina, alumina, and kieselguhr.
 5. The method ofclaim 4 wherein the hydrogenation catalyst comprises nickel and tungstensupported upon alumina.
 6. The method of claim 4 wherein thehydrogenation catalyst comprises cobalt and molybdenum supported uponaluMina.
 7. The method of claim 2 wherein the light fraction ishydrogenated at a temperature of from about 650*F to about 700*F, apressure of from about 1,500 psig to about 3,000 psig, a liquid hourlyspace velocity of from about 0.25 to about 1.5 volumes of oil per volumeof catalyst per hour, and a hydrogen rate of from about 5,000 to about20,000 standard cubic feet of hydrogen per barrel of light fraction. 8.The method of claim 7 wherein the hydrocracked lubricating oil stock isseparated into a light fraction having an initial boiling point of about600*F and an end point of about 725*F and a heavy fraction having aninitial boiling point of about 725*F by fractional distillation.
 9. Themethod of claim 8 wherein the initial boiling point temperature of thereblended oil is adjusted to about 600*F by vaporizing low boilingcracked hydrocarbons from the liquid reblended oil at an elevatedtemperature of about 340*F and a subatmospheric pressure of about 3millimeters mercury, absolute.